CDNA CLONING AND CHARACTERIZATION OF AN ALPHA-GLUCOSIDASE GENE FROM POTATO (SOLANUM-TUBEROSUM L.)

Using an Arabidopsis thaliana expressed sequence tag with sequence sim ilarity to human lysosomal cr-glucosidase as a probe, a potato cDNA wa s isolated. The cDNA encodes a polypeptide with an Mr value of 105,400 and the most significant matches of the deduced amino acid sequence a re with members of family 31 of glucosyl transferase. The potato cDNA was expressed in a strain of Saccharomyces cerevisiae that is deficien t in maltase activity and unable to grow using maltose as a carbon sou rce (ABYSMAL81). Expression of the potato cDNA in the mutant yeast str ain restores its ability to use maltose as a carbon source for growth. Additionally, a-glucosidase activity could be measured in extracts of the yeast cells following complementation. A range of maltodextrins w ere substrates for this activity. The steady-state expression level of the potato a-glucosidase gene was low in most tissues examined, the h ighest levels occurring in sprouting tubers and source leaves.